1. Field of the Invention
The present invention relates to a method for determining the color of an illuminant and an apparatus therefor, and more particularly, to a method for determining the color of an illuminant by estimating the color of an illuminant of an input image and an apparatus therefor.
2. Description of the Related Art
Color correction is performed, considering the influence of illumination during photography in a color image inputting apparatus such as a digital camera. A white balancing function for performing color correction with respect to a channel ratio among R, G, and B channels is widely used as a representative example of color correction with respect to an illuminant Various methods for performing color correction such as white balancing have been developed. In the case of a video camera, chrominance information of an illuminant is generally obtained by photographing white paper or a white board before photography and white balancing is performed with reference to the chrominance information. Alternatively, controlling buttons corresponding to specific illuminations may be included and the button input by a user may be referred to. Alternatively, an illumination detector may be attached to a camera and information on the illumination may be obtained from a detected signal. Alternatively, the color of an illuminant may be obtained from a photographed image. However, the method of using the photo detector has problems in that the manufacturing costs increase since additional hardware is required for the camera and it is difficult to use for an image obtained by remote photography. Also, the method of using buttons has a problem in that many buttons are necessary in order to appropriately correspond to various illuminant components.
A method according to a conventional technology for solving the above problems is provided in U.S. Pat. No. 4,685,071. According to the above method, the color of a specularly reflected light is detected in a scene of an image so that the color of the light used to illuminate the scene is determined. According to this method, the color of the specularly reflected light is detected by detecting a surrounding area which includes highlight displaying varying hues and saturations on a plurality of differently colored surfaces in the scene. Also, according to the method, an image is transformed into a color signal of a chrominance coordinate in order to detect the change of a color which is independent of brightness and color boundaries on which saturation and color most severely change. Then, the color of the illuminant is detected using a data set around the boundary due to the change in saturation. In this case, in order to determine whether the boundary is due to the change in saturation or due to color, the data sets positioned on both sides of the boundary are collected and approximated to straight lines and variables determined to be colors of illuminants are collected from the paths of the intersection points of the straight lines.
However, in this method, it is not easy to collect data since the data sets are not approximated to the straight lines and further to this it is required that collection data on both sides of the boundary point, approximating the data to straight lines, and comparing and determining the data must be repeated. Therefore, such a method has disadvantage in that it takes an excessively long time to perform.
A method according to another conventional technology is provided in the U.S. Pat. No. 5,495,428. According to this method, the color of an illuminant is determined by grasping the color distribution using a histogram with respect to the entire image, obtaining a direct line which becomes a main axis in each cluster, and applying an appropriate scale factor to each direct line. While in this method it is relatively easy to secure data to be processed, it requires a large amount of calculation during the process of interpreting though.